Relax, you already got second place.
How happy would you have felt about a guaranteed second before you started?
How much would you have wished for a second or even any cash if you had been knocked out early?
You've already done well, anything else is just the icing on the cake.
So with a relaxed frame of mind just carry on and see what happens.
There is a lot of luck in heads up, if you get good cards, good catches and suck outs you can't lose. Conversely even the best heads up players can do nothing about facing suck outs, catches and cards, so if you come up against it then you're stuck.
You could try to improve your heads up skills by reading or playing sit and go. This would improve your edge a bit and your confidence, familiarity, knowledge and nerves.